It is common to use either three or four springs to support a shadow mask within a rectangular faceplate panel of a color picture tube. In a three spring support system, one spring is usually located at the upper center of the mask, and the other two springs are located along the sides of the tube between the centers of the sides of the mask and the lower two corners of the mask. In a four-spring support system, springs are usually located at the top and bottom centers of the mask and at the left and right centers of the mask. In both the three- and four-spring support systems, as described above, it is possible for the shadow mask to slightly twist and shift relative to the faceplate during manufacturing and tube operation.
One means for minimizing twisting and shifting of a shadow-mask uses spring supports at the four corners of the frame. Embodiments for achieving such corner support are shown in U.S. Pat. No. 4,723,088, issued to Sone et al. on Feb. 2, 1988, and in U.S. Pat. No. 4,728,853, issued to Sone et al. on Mar. 1, 1988.
U.S. Pat. No. 4,723,088 shows a shadow mask frame having truncated corners with supports at each corner. The supports are bent plates including three sections. A first section is welded to the frame. A second section extends at an angle from the first section toward a skirt of a faceplate panel. A third section extends from the second section. The third section includes an aperture that engages a metal stud that is embedded in the panel sidewall.
U.S. Pat. No. 4,728,853 discloses an improved support which includes two members welded together. One member, having a flat plate shape, is welded to a mask frame. The second member includes three sections. A first section is welded to the first member. A second section angles from the first section, and an apertured third section engages a support stud in the panel sidewall.
FIG. 4 of U.S. Pat. No. 4,723,088 shows a mask-frame assembly having the support means aligned with the diagonals of the assembly. The embodiment shown has a 4 by 3 aspect ratio. When tubes having a 16 by 9 aspect ratio were recently developed, it was decided to utilize the corner support concept and to align the mask support means with the diagonals. However, tubes so constructed exhibited substantial electron beam misregister when they were subjected to vibration and/or shock. Such misregister also occurred in tubes having a 4 by 3 aspect ratio but to a lesser extent. Therefore, there is a need for an improved mask mounting system that will minimize vibration misregister and provide a better response to shock. Such improvement is especially needed in tubes having a 16 by 9 aspect ratio, but should also provide some improvement in tubes having a 4 by 3 aspect ratio.